The most important incentive to scientific fraud is a passionate belief in the truth and significance of a theory or hypothesis which is disregarded or frankly not believed by the majority of scientists

From Science Fictions by Stuart Ritchie.  Page 71.

Another motive may be the fraudster’s pathologically mistaken views on what science is about. The immunologist and Nobelist Sir Peter Medawar has argued, perhaps counter-intuitively, that scientists who commit fraud care too much about the truth, but that their idea of what’s true has become disconnected from reality. ‘I believe,’ he wrote, ‘that the most important incentive to scientific fraud is a passionate belief in the truth and significance of a theory or hypothesis which is disregarded or frankly not believed by the majority of scientists – colleagues who must accordingly be shocked into recognition of what the offending scientist believes to be a self-evident truth.’ The physicist David Goodstein agrees: ‘Injecting falsehoods into the body of science is rarely, if ever, the purpose of those who perpetrate fraud,’ he suggests. ‘They almost always believe that they are injecting a truth into the scientific record … but without going through all the trouble that the real scientific method demands.’

See Eirc Hoffer's The True Believer for greater explication  of this dangerous condition which is far more prevalent than it used to be.  People who determine truth based on their emotional convictions rather than the evidence.